Aerial lifts of the type including an articulated boom supporting an operator platform or bucket, may also include a jib and winch supported at the end of the boom and permitting the operator to lift and support various loads such as equipment to be installed by an operator supported in the bucket.
In operation of the aerial lift, and particularly aerial lifts including a jib and winch for lifting utility equipment or the like, it is important that the operator not overload the aerial lift boom by attempting to lift an object of excessive weight or an object which may be obstructed. For example, in cold climates an object to be lifted may be frozen in place thereby placing a substantial unexpected load on the aerial lift. Additionally, when the aerial lift bucket is supporting a load, during operation of the aerial lift, the upper boom may move from a first position wherein the length of the moment arm of the vertical force of the load on the boom is sufficiently short that the boom is not overloaded, to a second position wherein the length of the moment arm increases and the load on the boom then exceeds the maximum acceptable load on the boom assembly.
Because the load on the boom is dependent both on the weight of the objects being lifted and the relative position of the upper boom with respect horizontal, successful load sensing systems or overload alarm systems have not been developed.